This invention relates to the stabilization of microbicides. In particular, this invention relates to the improved stabilization of 3-isothiazolone microbicides.
Microbicides are used commercially to prevent the growth of microbes in a variety of loci, such as cooling towers, metal working fluid systems, paint and cosmetics. One of the more important classes of microbicides is 3-isothiazolones. Many 3-isothiazolones have achieved commercial success because they are very effective in preventing microbial growth under a wide variety of conditions and in a variety of loci. Among the most important 3-isothiazolones are 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone, and mixtures thereof.
While 3-isothiazolones are very effective microbicides, they suffer from being unstable under certain conditions. Without the presence of a stabilizer, many 3-isothiazolones chemically degrade and lose microbicidal efficacy. Much research has been devoted to stabilizing 3-isothiazolones.
Typical 3-isothiazolone products of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain between 1 and 25 percent by weight of the 3-isothiazolone mixture and a similar amount of a stabilizer. Concentrate compositions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone generally contain about 5 to 35 percent by weight of the 3-isothiazolone compounds and require about 10 to 25 percent by weight of a stabilizer. Dilute solutions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain about 0.5 to 5 percent by weight of the 3-isothiazolone compounds. In general, the compounds that stabilize 3-isothiazolone concentrates do not stabilize 3-isothiazolone dilute solutions. Compounds, such as magnesium nitrate, that do stabilize both 3-isothiazolone concentrates and dilute solutions do so in greatly differing amounts. More magnesium nitrate is required to stabilize a 3-isothiazolone dilute solution than a concentrate, 23 percent by weight for dilute solutions as compared to 12 to 16 percent by weight for concentrates. As dilute solutions are typically prepared by diluting 3-isothiazolone concentrate compositions, this need for additional stabilizer results in increased costs and handling.
Various stabilizers are known for 3-isothiazolones; however, these stabilizers suffer from providing a high metal salt content or providing only limited stability to the 3-isothiazolone. When a 3-isothiazolone stabilized with a metal salt is added to a latex formulation, the high metal salt content can coagulate the latex. JP 05 170 608 A discloses bromic acid, iodic acid, periodic acid or their salts as stabilizers for 3-isothiazolone compositions. This patent application teaches the replacement of bivalent metal salts, such as magnesium nitrate, as stabilizers with bromic acid, iodic acid, periodic acid or their salts. This is not a complete solution to the stability issue, as iodate and periodate salts provide little to no stability for those 3-isothiazolone compositions having a concentration of 10 to 35 percent by weight. This patent application also does not address the problem of precipitate formation upon storage of the 3-isothiazolone compositions.
Although the use of stabilizers, such as metal nitrate salts, enables 3-isothiazolone products to retain their microbicidal efficacy for considerable periods of time, other problems may develop without significant loss of 3-isothiazolones, such as the formation of precipitate upon storage. The presence of this precipitate does not impact the efficacy of the 3-isothiazolones; however, the presence of the precipitate gives undesirable appearance to users of the product. It is clearly preferable from a commercial standpoint to have a product which does not form a precipitate.
Thus, there is a continuing need for stable 3-isothiazolone concentrate compositions that remain stable when diluted to form dilute solutions without the need for additional stabilizer and are free of undesirable precipitate.